Challenges and opportunities for siRNA-based cancer treatment

As one of the life-threatening diseases involving multi-step genetic and epigenetic disorders, cancer has long been a dynamic research area for siRNA-based therapy as half of the current siRNA-based clinical trials are involved in oncology. However, despite consistent enthusiasm in the academic world, siRNA-based cancer treatment still faces obstacles and difficulties in clinical development. In this article, we discuss key challenges facing siRNA-based cancer treatment revealed from recent clinical and preclinical studies, including chemical modification, tumour penetration, endosomal escape, target selection and off-target effects. In addition, opportunities and avenues for translating siRNA technology from bench to oncologic clinics are explored.

pH-Responsive Polymer Conjugate of Pirarubicin With Styrene Maleic Acid Copolymer as a Potential Therapeutic for Ovarian Cancer

Previous studies indicated the potential of styrene maleic acid copolymer (SMA)-conjugated pirarubicin (4'-O-tetrahydropyranyldoxorubicin [THP]) for targeted anticancer therapy based on the enhanced permeability and retention effect. In this study, to achieve further improved therapeutic efficacy, a pH-responsive SMA-conjugated THP-containing hydrazone bond (SMA-hyd-THP) was synthesized and evaluated in vitro and ex vivo using human ovarian cancer cells and tissues. SMA-hyd-THP showed good water solubility, forming micelles with a mean particle size of 48.0 nm, which is applicable for enhanced permeability and retention-based tumor accumulation. The THP loading in this preparation was 15% (wt/wt), and release rate of free THP from SMA-hyd-THP at physiological pH (7.4) was approximately 10% in 72 h. However, it increased rapidly at pH 6.5 (42%) and 5.5 (83%), which indicates that tumor environment of weak acidic condition (pH 6.5-6.9) is favorable for release of THP. This notion was partly proved by incubating SMA-hyd-THP with tumor tissues from ovarian cancer patients. In addition, release of THP was not affected by serum, suggesting that SMA-hyd-THP is relatively stable in circulation. Finally, SMA-hyd-THP showed much increased cytotoxicity against various ovarian cancer cells at acidic tumor pH (6.5). These findings may provide an option for targeted therapy against ovarian cancer.

Early diagnosis of lymph node metastasis: Importance of intranodal pressures

Regional lymph node status is an important prognostic indicator of tumor aggressiveness. However, early diagnosis of metastasis using intranodal pressure, at a stage when lymph node size has not changed significantly, has not been investigated. Here, we use an MXH10/Mo-lpr/lpr mouse model of lymph node metastasis to show that intranodal pressure increases in both the subiliac lymph node and proper axillary lymph node, which are connected by lymphatic vessels, when tumor cells are injected into the subiliac lymph node to induce metastasis to the proper axillary lymph node. We found that intranodal pressure in the subiliac lymph node increased at the stage when metastasis was detected by in vivo bioluminescence, but when proper axillary lymph node volume (measured by high-frequency ultrasound imaging) had not increased significantly. Intravenously injected liposomes, encapsulating indocyanine green, were detected in solid tumors by in vivo bioluminescence, but not in the proper axillary lymph node. Basic blood vessel and lymphatic channel structures were maintained in the proper axillary lymph node, although sinus histiocytosis was detected. These results show that intranodal pressure in the proper axillary lymph node increases at early stages when metastatic tumor cells have not fully proliferated. Intranodal pressure may be a useful parameter for facilitating early diagnosis of lymph node metastasis.

Photodynamic Graphene Quantum Dot: Reduction Condition Regulated Photoactivity and Size Dependent Efficacy

Prequenching and selective activation of photosensitizer (PS) are highly desired in photodynamic therapy (PDT) to avoid off-target effect due to nonspecific activation and poor targeting selectivity of PS. In this study, nanographene materials as a unique π-conjugated planar system for electronic transfer were employed as the robust platform for temporarily quenching of PS. Photosensitizer chlorin e6 (Ce6) was integrated onto planar structure of graphene quantum dot (GQD) or graphene oxide (GO) via a reduction cleavable disulfide linker. The formed hybrid nanosystem displayed considerable fluorescence quenching and slight phototoxicity, even under the condition of light irradiation, while the photoactivity of PS could be selectively recovered in the presence of the reducing agent. Compared with graphene oxide system with larger size (around 200 nm), GQD nanosystem exhibited significantly improved tumor accumulation via enhanced permeation and retention effect (EPR effect). The in vivo study demonstrated extremely effective suppression of tumor growth for the group treated with the GQD nanosystem with cleavable linker, revealing the promising application of the presented novel strategy.

Pretargeted Positron Emission Tomography Imaging That Employs Supramolecular Nanoparticles with in Vivo Bioorthogonal Chemistry

A pretargeted oncologic positron emission tomography (PET) imaging that leverages the power of supramolecular nanoparticles with in vivo bioorthogonal chemistry was demonstrated for the clinically relevant problem of tumor imaging. The advantages of this approach are that (i) the pharmacokinetics (PKs) of tumor-targeting and imaging agents can be independently altered via chemical alteration to achieve the desired in vivo performance and (ii) the interplay between the two PKs and other controllable variables confers a second layer of control toward improved PET imaging. In brief, we utilized supramolecular chemistry to synthesize tumor-targeting nanoparticles containing transcyclooctene (TCO, a bioorthogonal reactive motif), called TCO⊂SNPs. After the intravenous injection and subsequent concentration of the TCO⊂SNPs in the tumors of living mice, a small molecule containing both the complementary bioorthogonal motif (tetrazine, Tz) and a positron-emitting radioisotope ((64)Cu) was injected to react selectively and irreversibly to TCO. High-contrast PET imaging of the tumor mass was accomplished after the rapid clearance of the unreacted (64)Cu-Tz probe. Our nanoparticle approach encompasses a wider gamut of tumor types due to the use of EPR effects, which is a universal phenomenon for most solid tumors.

Enhancement of Tumor-Targeted Delivery of Bacteria with Nitroglycerin Involving Augmentation of the EPR Effect

The use of bacteria, about 1 μm in size, is now becoming an attractive strategy for cancer treatment. Solid tumors exhibit the enhanced permeability and retention (EPR) effect for biocompatible macromolecules such as polymer-conjugated anticancer agents, liposomes, and micelles. This phenomenon permits tumor-selective delivery of such macromolecules. We report here that bacteria injected intravenously evidenced a property similar to that can of these macromolecules. Bacteria that can accumulate selectively in tumors may therefore be used in cancer treatment.Facultative or anaerobic bacteria will grow even under the hypoxic conditions present in solid tumors. We found earlier that nitric oxide (NO) was among the most important factors that facilitated the EPR effect via vasodilatation, opening of endothelial cell junction gaps, and increasing the blood flow of hypovascular tumors. Here, we describe the augmentation of the EPR effect by means of nitroglycerin (NG), a commonly used NO donor, using various macromolecular agents in different tumor models. More importantly, we report that NG significantly enhanced the delivery of Lactobacillus casei to tumors after intravenous injection of the bacteria, more than a tenfold increase in bacterial accumulation in tumors after NG treatment. This finding suggests that NG has a potential advantage to enhance bacterial therapy of cancer, and further investigations of this possibility are warranted.

Recent advances in polymeric micelles for anti-cancer drug delivery

Block co-polymeric micelles receive increased attention due to their ability to load therapeutics, deliver the cargo to the site of action, improve the pharmacokinetic of the loaded drug and reduce off-target cytotoxicity. While polymeric micelles can be developed with improved drug loading capabilities by modulating hydrophobicity and hydrophilicity of the micelle forming block co-polymers, they can also be successfully cancer targeted by surface modifying with tumor-homing ligands. However, maintenance of the integrity of the self-assembled system in the circulation and disassembly for drug release at the site of drug action remain a challenge. Therefore, stimuli-responsive polymeric micelles for on demand drug delivery with minimal off-target effect has been developed and extensively investigated to assess their sensitivity. This review focuses on discussing various polymeric micelles currently utilized for the delivery of chemotherapeutic drugs. Designs of various stimuli-sensitive micelles that are able to control drug release in response to specific stimuli, either endogenous or exogenous have been delineated.

Investigation of Factors Determining the Enhanced Permeability and Retention Effect in Subcutaneous Xenografts

Liposomal chemotherapy offers several advantages over conventional therapies, including high intratumoral drug delivery, reduced side effects, prolonged circulation time, and the possibility to dose higher. The efficient delivery of liposomal chemotherapeutics relies, however, on the enhanced permeability and retention (EPR) effect, which refers to the ability of macromolecules to extravasate leaky tumor vessels and accumulate in the tumor tissue. Using a panel of human xenograft tumors, we evaluated the influence of the EPR effect on liposomal distribution in vivo by injection of pegylated liposomes radiolabeled with (111)In. Liposomal accumulation in tumors and organs was followed over time by SPECT/CT imaging. We observed that fast-growing xenografts, which may be less representative of tumor development in patients, showed higher liposomal accumulation than slow-growing xenografts. Additionally, several other parameters known to influence the EPR effect were evaluated, such as blood and lymphatic vessel density, intratumoral hypoxia, and the presence of infiltrating macrophages. The investigation of various parameters showed a few correlations. Although hypoxia, proliferation, and macrophage presence were associated with tumor growth, no hard conclusions or predictions could be made regarding the EPR effect or liposomal uptake. However, liposomal uptake was significantly correlated with tumor growth, with fast-growing tumors showing a higher uptake, although no biological determinants could be elucidated to explain this correlation.

Intra-tumor distribution of PEGylated liposome upon repeated injection: No possession by prior dose

Liposomes have proven to be a viable means for the delivery of chemotherapeutic agents to solid tumors. However, significant variability has been detected in their intra-tumor accumulation and distribution, resulting in compromised therapeutic outcomes. We recently examined the intra-tumor accumulation and distribution of weekly sequentially administered oxaliplatin (l-OHP)-containing PEGylated liposomes. In that study, the first and second doses of l-OHP-containing PEGylated liposomes were distributed diversely and broadly within tumor tissues, resulting in a potent anti-tumor efficacy. However, little is known about the mechanism underlying such a diverse and broad liposome distribution. Therefore, in the present study, we investigated the influence of dosage interval on the intra-tumor accumulation and distribution of "empty" PEGylated liposomes. Intra-tumor distribution of sequentially administered "empty" PEGylated liposomes was altered in a dosing interval-dependent manner. In addition, the intra-tumor distribution pattern was closely related to the chronological alteration of tumor blood flow as well as vascular permeability in the growing tumor tissue. These results suggest that the sequential administrations of PEGylated liposomes in well-spaced intervals might allow the distribution to different areas and enhance the total bulk accumulation within tumor tissue, resulting in better therapeutic efficacy of the encapsulated payload. This study may provide useful information for a better design of therapeutic regimens involving multiple administrations of nanocarrier drug delivery systems.

Design considerations for nanotherapeutics in oncology

Nanotherapeutics have improved the quality of life of cancer patients, primarily by reducing the adverse effects of chemotherapeutic agents, but improvements in overall survival are modest. This is in large part due to the fact that the enhanced permeability and retention effect, which is the basis for the use of nanoparticles in cancer, can be also a barrier to the delivery of nanomedicines. A careful design of nanoparticle formulations can overcome barriers posed by the tumor microenvironment and result in better treatments. In this review, we first discuss strengths and limitations of clinically-approved nanoparticles. Then, we evaluate design parameters that can be modulated to optimize delivery. The benefits of active tumor targeting and drug release rate on intratumoral delivery and treatment efficacy are also discussed. Finally, we suggest specific design strategies that should optimize delivery to most solid tumors and discuss under what conditions active targeting would be beneficial.

FROM THE CLINICAL EDITOR

Advances in nanotechnology have seen the introduction of new treatment modalities for cancer. The principle of action using nanocarriers for drug delivery is based mostly on the Enhanced Permeability and Retention effect. This phenomenon however, can also be a hindrance. In this article, the authors performed an in-depth review on various nanoparticle platforms in cancer therapeutics. They also suggested options to improve drug delivery, in terms of carrier design.

pH sensitive polymeric complex of cisplatin with hyaluronic acid exhibits tumor-targeted delivery and improved in vivo antitumor effect

Cisplatin (CDDP) is widely used anticancer drug for various solid tumors including lung cancer. However, its indiscriminate distribution causes serious adverse effects and limits its therapeutic effect. In this study, by using hyaluronic acid (HA) we synthesized a complex of CDDP (HA-CDDP), by utilizing ionic interaction between Pt(2+) of CDDP with carboxyl group of HA. The mean HA-CDDP particle size was 208.5nm in PBS according to dynamic light scattering which was also confirmed by TEM, which could exert tumor-targeting property by enhanced permeability and retention (EPR) effect. The CDDP loading in this preparation was 13% (w/w), and release rate of free CDDP from the HA-CDDP complex at physiological pH (7.4) was ∼20%/day. However, in acidic pH the release was much faster, i.e., ∼95% of CDDP was released in 72h at pH 5.5. Moreover, HA-CDDP showed a 2.5-fold higher tumor accumulation than free CDDP whereas no increase of distribution was found in most normal tissues. In addition, because HA receptor CD44 is overexpressed in many tumor cells, we also observed CD44-based endocytosis of HA-CDDP in mouse lung carcinoma LCC cells. These findings together suggest that HA-CDDP may show tumor-selective cytotoxicity by taking advantage of EPR effect, weak acidic environment of tumor tissues (e.g., pH 6∼7), as well as CD44-based intracellular uptake. As expected, HA-CDDP exhibited much improved therapeutic effect than free CDDP in mouse LCC tumor model, whereas no apparent side effect was found. These findings may shed some light on the potential utility of HA for development of tumor-targeted polymeric CDDP drugs, which need further investigations.

Repurposing Drugs in Oncology (ReDO)-nitroglycerin as an anti-cancer agent

Nitroglycerin (NTG), a drug that has been in clinical use for more than a century, has a range of actions which make it of particular interest in an oncological setting. It is generally accepted that the main mechanism of action of NTG is via the production of nitric oxide (NO), which improves cardiac oxygenation via multiple mechanisms including improved blood flow (vasodilation), decreased platelet aggregation, increased erythrocyte O2 release and decreased mitochondrial utilization of oxygen. Its vasoactive properties mean that it has the potential to exploit more fully the enhanced permeability and retention effect in delivering anti-cancer drugs to tumour tissues. Moreover NTG can reduce HIF-1α levels in hypoxic tumour tissues and this may have anti-angiogenic, pro-apoptotic and anti-efflux effects. Additionally NTG may enhance anti-tumour immunity. Pre-clinical and clinical data on these anti-cancer properties of NTG are summarised and discussed. While there is evidence of a positive action as a monotherapy in prostate cancer, there are mixed results in NSCLC where initially positive results have yet to be fully replicated. Based on the evidence presented, a case is made that further exploration of the clinical benefits that may accrue to cancer patients is warranted. Additionally, it is proposed that NTG may synergise with a number of other drugs, including other repurposed drugs, and these are discussed in the supplementary material appended to this paper.

Styrene-maleic acid-copolymer conjugated zinc protoporphyrin as a candidate drug for tumor-targeted therapy and imaging

Previous studies indicated the potential of zinc protoporphyrin (ZnPP) as an antitumor agent targeting to the tumor survival factor heme oxygenase-1, and/or for photodynamic therapy (PDT). In this study, to achieve tumor-targeted delivery, styrene-maleic acid-copolymer conjugated ZnPP (SMA-ZnPP) was synthesized via amide bond, which showed good water solubility, having ZnPP loading of 15%. More importantly, it forms micelles in aqueous solution with a mean particle size of 111.6 nm, whereas it has an apparent Mw of 65 kDa. This micelle formation was not detracted by serum albumin, suggesting it is stable in circulation. Further SMA-ZnPP conjugate will behave as an albumin complex in blood with much larger size (235 kDa) by virtue of the albumin binding property of SMA. Consequently, SMA-ZnPP conjugate exhibited prolonged circulating retention and preferential tumor accumulation by taking advantage of enhanced permeability and retention (EPR) effect. Clear tumor imaging was thus achieved by detecting the fluorescence of ZnPP. In addition, the cytotoxicity and PDT effect of SMA-ZnPP conjugate was confirmed in human cervical cancer HeLa cells. Light irradiation remarkably increased the cytotoxicity (IC50, from 33 to 5 μM). These findings may provide new options and knowledge for developing ZnPP based anticancer theranostic drugs.

Synthesis and evaluation of MePEG-PCL diblock copolymers: surface properties and controlled release behavior

The amphiphilic block copolymers are composed of various combinations of hydrophilic and hydrophobic block unimers. The variation in unimer ratio alters the surface as well as micelle-forming properties of the block copolymers. These nanoscopic micelles have the ability to encapsulate hydrophobic compounds and act as potential drug carrier. MePEG-PCL copolymers with various block lengths were synthesized by ring-opening polymerization and characterized by ¹HNMR, GPC, WXRD and DSC. The number average molecular weight of the block copolymer was found to vary from 7511 to 21,270 as determined by GPC and ¹HNMR studies. The surface topology of the polymer films was determined by AFM analysis, which shows a smoother surface with increased MePEG contents in the block copolymers. The protein-binding assay indicates a better biocompatibility of the block copolymers in comparison to MePEG or PCL alone. The CMC of the block copolymer provides the information about micelle formations for encapsulation of hydrophobic materials and affects the in vitro release.

Peptides and proteins used to enhance gold nanoparticle delivery to the brain: preclinical approaches

An exciting and emerging field in nanomedicine involves the use of gold nanoparticles (AuNPs) in the preclinical development of new strategies for the treatment and diagnosis of brain-related diseases such as neurodegeneration and cerebral tumors. The treatment of many brain-related disorders with AuNPs, which possess useful physical properties, is limited by the blood–brain barrier (BBB). The BBB highly regulates the substances that can permeate into the brain. Peptides and proteins may represent promising tools to improve the delivery of AuNPs to the central nervous system (CNS). In this review, we summarize the potential applications of AuNPs to CNS disorders, discuss different strategies based on the use of peptides or proteins to improve the delivery of AuNPs to the brain, and examine the intranasal administration route, which bypasses the BBB. We also analyze the potential neurotoxicity of AuNPs and the perspectives and new challenges concerning the use of peptides and proteins to enhance the delivery of AuNPs to the brain. The majority of the work described in this review is in a preclinical stage of experimentation, or in select cases, in clinical trials in humans. We note that the use of AuNPs still requires substantial study before being translated into human applications. However, for further clinical research, the issues related to the potential use of AuNPs must be analyzed.

Sequential combination therapy of ovarian cancer with degradable N-(2-hydroxypropyl)methacrylamide copolymer paclitaxel and gemcitabine conjugates

For rapid and effective clinical translation, polymer-based anticancer therapeutics need long circulating conjugates that produce a sustained concentration gradient between the vasculature and solid tumor. To this end, we designed second-generation backbone-degradable diblock N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer carriers and evaluated sequential combination therapy of HPMA copolymer-paclitaxel and HPMA copolymer-gemcitabine conjugates against A2780 human ovarian carcinoma xenografts. First, extensive in vitro assessment of administration sequence impact on cell cycle, viability, apoptosis, migration, and invasion revealed that treatment with paclitaxel conjugate followed by gemcitabine conjugate was the most effective scheduling strategy. Second, in an in vivo comparison with first-generation (nondegradable, molecular weight below the renal threshold) conjugates and free drugs, the second-generation degradable high-molecular weight conjugates showed distinct advantages, such as favorable pharmacokinetics (three- to five-times half-life compared with the first generation), dramatically enhanced inhibition of tumor growth (complete tumor regression) by paclitaxel and gemcitabine conjugate combination, and absence of adverse effects. In addition, multimodality imaging studies of dual-labeled model conjugates confirmed the efficacy of second-generation conjugates by visualizing more than five-times enhanced tumor accumulation, rapid conjugate internalization, and effective intracellular release of payload. Taken together, the results indicate that the second-generation degradable HPMA copolymer carrier can provide an ideal platform for the delivery of a range of antitumor compounds, which makes it one of the most attractive candidates for potential clinical application.

Enhanced bacterial tumor delivery by modulating the EPR effect and therapeutic potential of Lactobacillus casei

Bacteria of micrometer size could accumulate in tumor based on enhanced permeability and retention (EPR) effect. We report here Lactobacillus casei (L. casei), a nonpathogenic facultatively anaerobic bacterium, preferentially accumulated in tumor tissues after intravenously (i.v.) injection; at 24 h, live bacteria were found more in the tumor, whereas the bacteria in normal tissues including the liver and spleen were cleared rapidly. The tumor-selective accumulation and growth of L. casei is probably due to the EPR effect and the hypoxic tumor environment. Moreover, the bacterial tumor delivery was significantly increased by a nitric oxide (NO) donor nitroglycerin (NG, 10-70 times) and an angiotensin II converting enzyme inhibitor, enalapril (6-18 times). Consequently significant suppression of tumor growth was found in a colon cancer C26 model, and more remarkable antitumor effect was achieved when L. casei was combined with NG, probably by modulating the host nonspecific immune responses; tumor necrosis factor-α significantly increased in tumor after the treatment, as well as NO synthase activity and myleoperoxidase activity. These findings suggest the potential of L. casei as a candidate for targeted bacterial antitumor therapy, especially in combine with NG or other vascular mediators.

Inhibition of ectopic glioma tumor growth by a potent ferrocenyl drug loaded into stealth lipid nanocapsules

In this work, a novel ferrocenyl complex (ansa-FcdiOH) was assessed for brain tumor therapy through stealth lipid nanocapsules (LNCs). Stealth LNCs, prepared according to a one-step process, showed rapid uptake by cancer cells and extended blood circulation time. The ferrocenyl complex was successfully encapsulated into these LNCs measuring 40 nm with a high loading capacity (6.4%). In vitro studies showed a potent anticancer effect of ansa-FcdiOH on 9L cells with a low IC50 value (0.1 μM) associated with an oxidative stress and a dose-dependent alteration of the cell cycle. Repeated intravenous injections of stealth ansa-FcdiOH LNCs in ectopic glioma bearing rats induced a significant tumor growth inhibition, supported by a reduced number of proliferative cells in tumors compared to control group. Additionally, no liver damage was observed in treated animals. These results indicated that stealth ansa-FcdiOH LNCs might be considered as a potential new approach for cancer chemotherapy.

FROM THE CLINICAL EDITOR

In this study, a novel ferrocenyl complex was assessed for brain tumor therapy through stealth lipid nanocapsules, demonstrating no liver damage, and superior tumor volume reduction compared to saline and stealth lipid nanocapsules alone in an ectopic glioma model.

Serum biomarkers for personalization of nanotherapeutics-based therapy in different tumor and organ microenvironments

Enhanced permeation and retention (EPR) effect, the mechanism by which nanotherapeutics accumulate in tumors, varies in patients based on differences in the tumor and organ microenvironment. Surrogate biomarkers for the EPR effect will aid in selecting patients who will accumulate higher amounts of nanotherapeutics and show better therapeutic efficacy. Our data suggest that the differences in the vascular permeability and pegylated liposomal doxorubicin (PLD) accumulation are tumor type as well as organ-specific and significantly correlated with the relative ratio of MMP-9 to TIMP-1 in the circulation, supporting development of these molecules as biomarkers for the personalization of nanoparticle-based therapy.

Two step mechanisms of tumor selective delivery of N-(2-hydroxypropyl)methacrylamide copolymer conjugated with pirarubicin via an acid-cleavable linkage

N-(2-Hydroxypropyl)methacrylamide copolymer containing hydrazide groups (PHPMA) conjugated with pirarubicin (THP) via a hydrazone bond (PHPMA-hyd-THP) is a drug conjugate that releases THP in the acidic milieu of a tumor. PHPMA-hyd-THP has an apparent Mw of 40,000 and a hydrodynamic diameter of 8.2±1.7nm but no apparent plasma protein binding. PHPMA-hyd-THP possesses two mechanisms of selectivity toward solid tumors and has potent antitumor action. The first one is drug accumulation in tumors that depends on the enhanced permeability and retention (EPR) effect, which results in a 4-20 times higher concentration of drug in the tumor than in normal tissues such as the heart, lung, and intestine. This accumulation in tumor tissue is in great contrast to that of conventional low-Mw THP. The second one is pH-dependent release of drug from PHPMA-hyd-THP: this conjugate released free THP more efficiently at a lower pH, which exists in tumors, and exerts cytotoxic activity. Free THP is known for its much faster uptake into tumor cells compared with doxorubicin. Thus, in our in vitro study, PHPMA-hyd-THP showed a higher cytotoxicity at the lower pH of tumor tissue than at the neutral pH of normal tissue. Furthermore, much more THP was liberated from the conjugate in acidic tumor tissue than in normal tissue. The EPR effect-dependent accumulation of PHPMA-hyd-THP and tumor-selective THP release in the tumor tissues led to highly tumor-selective drug accumulation, which continued for more than 72h, whereas the lowest free drug concentration was detected in normal tissues at 24h and no longer at a later time. In conclusion, we determined in our study here that the acid-cleavable PHPMA-hyd-THP conjugate had an excellent antitumor effect without appreciable adverse effects.

Ligand-targeted liposome design: challenges and fundamental considerations

Nanomedicine, particularly liposomal drug delivery, has expanded considerably over the past few decades, and several liposomal drugs are already providing improved clinical outcomes. Liposomes have now progressed beyond simple, inert drug carriers and can be designed to be highly responsive in vivo, with active targeting, increased stealth, and controlled drug-release properties. Ligand-targeted liposomes (LTLs) have the potential to revolutionize the treatment of cancer. However, these highly engineered liposomes generate new problems, such as accelerated clearance from circulation, compromised targeting owing to non-specific serum protein binding, and hindered tumor penetration. This article highlights recent challenges facing LTL strategies and describes the advanced design elements used to circumvent them.

Imaging and modification of the tumor vascular barrier for improvement in magnetic nanoparticle uptake and hyperthermia treatment efficacy

The predicted success of nanoparticle based cancer therapy is due in part to the presence of the inherent leakiness of the tumor vascular barrier, the so called enhanced permeability and retention (EPR) effect. Although the EPR effect is present in varying degrees in many tumors, it has not resulted in the consistent level of nanoparticle-tumor uptake enhancement that was initially predicted. Magnetic/iron oxide nanoparticles (mNPs) have many positive qualities, including their inert/nontoxic nature, the ability to be produced in various sizes, the ability to be activated by a deeply penetrating and nontoxic magnetic field resulting in cell-specific cytotoxic heating, and the ability to be successfully coated with a wide variety of functional coatings. However, at this time, the delivery of adequate numbers of nanoparticles to the tumor site via systemic administration remains challenging. Ionizing radiation, cisplatinum chemotherapy, external static magnetic fields and vascular disrupting agents are being used to modify the tumor environment/vasculature barrier to improve mNP uptake in tumors and subsequently tumor treatment. Preliminary studies suggest use of these modalities, individually, can result in mNP uptake improvements in the 3-10 fold range. Ongoing studies show promise of even greater tumor uptake enhancement when these methods are combined. The level and location of mNP/Fe in blood and normal/tumor tissue is assessed via histopathological methods (confocal, light and electron microscopy, histochemical iron staining, fluorescent labeling, TEM) and ICP-MS. In order to accurately plan and assess mNP-based therapies in clinical patients, a noninvasive and quantitative imaging technique for the assessment of mNP uptake and biodistribution will be necessary. To address this issue, we examined the use of computed tomography (CT), magnetic resonance imaging (MRI), and Sweep Imaging With Fourier Transformation (SWIFT), an MRI technique which provides a positive iron contrast enhancement and a reduced signal to noise ratio, for effective observation and quantification of Fe/mNP concentrations in the clinical setting.

Evaluating the potential of polymer nanoparticles for oral delivery of paclitaxel in drug-resistant cancer

The present study was designed to explore the ability of polymeric nanoparticles to restore drug sensitivity to P-glycoprotein over-expressing cancer cells. A multidrug-resistant cell line 2780 AD and its sensitive parent cell line A2780 were studied in cell culture and as a xenografted tumour model. Paclitaxel was incorporated in poly(lactide-co-glycolide) nanoparticles of average diameter 125 nm stabilised by a positively charged surfactant. The nanoparticulate formulation was shown to be about sevenfold more potent than free paclitaxel against cell line A2780 and the poly(lactic-co-glycolic acid) (PLGA) nanoparticles alone were nontoxic to the cells at the concentrations required to deliver the drug. Whilst the oral formulation of paclitaxel was not as potent as the free drug in the A2780 xenografts, it showed significant activity against 2780 AD tumours, which are resistant to the maximum tolerated intravenous dose of paclitaxel. The efficacy of orally delivered paclitaxel in this drug-resistant model supports the concept of exploring nanoparticles for improved drug delivery.